A duct heater is a structure designed to be inserted into an existing duct for heating air flowing through it. Duct heaters are very convenient in that they may be inserted into existing systems easily by removing a section of the duct, inserting the heater, and replacing the duct section. This type of heater is efficient in that only air flowing to a selected part of the system is heated because the various duct heaters may be separately energized. In some sections of the world, duct heaters represent a preferred method of heating.
U.S. Pat. No. 3,794,810 (Brasch et al) shows a heater for a circular duct wherein a support structure extends from a side of the duct into a central region. A heater element is supported by the structure and lies in a plane transverse to the flow of air in the duct. This apparatus requires a hole to be cut in the side of the duct and an adapter plate to be secured to the duct by screws.
U.S. Pat. Nos. 4,350,872 (Meywald et al) and 4,225,775 (Carter) show heaters wherein heating coils or ribbons are wrapped about the edges of outwardly extending support members.
U.S. Pat. No. 2,710,907 (Westberg et al) shows a heater which includes a duct section having a plurality of slots in its outer wall. A heating element is supported within the duct adjacent the slot, and a fan is placed at one end of the duct to pull air through the slots past the heating element.
U.S. Pat. No. 3,116,394 (Barton) shows a heater having a rectangular outer housing which supports a plurality of circular heating elements. The heating elements are modular, and any desired number may be attached together and supported within the rectangular housing.
U.S. Pat. No. 3,860,789 (Maake) shows a heating assembly wherein end portions are separated by intermediate beams, and flat insulating supports are attached to the intermediate beams. The heating coil element is then wound around the insulating supports. The end brackets are generally rectangular with the intermediate beams being attached at the corners of the rectangle. The end brackets have supporting feet for engaging projecting retaining rods in the apparatus where the assembly is to be used.